Semiconductor device with an oxygen diffusion barrier layer formed from a composite nitride

ABSTRACT

An impurity diffusion layer serving as the source or the drain of a transistor is formed in a semiconductor substrate, and a protection insulating film is formed so as to cover the transistor. A capacitor lower electrode, a capacitor dielectric film of an oxide dielectric film and a capacitor upper electrode are successively formed on the protection insulating film. A plug for electrically connecting the impurity diffusion layer of the transistor to the capacitor lower electrode is buried in the protection insulating film. An oxygen barrier layer is formed between the plug and the capacitor lower electrode. The oxygen barrier layer is made from a composite nitride that is a mixture or an alloy of a first nitride having a conducting property and a second nitride having an insulating property.

BACKGROUND OF THE INVENTION

The present invention relates to a semiconductor device including acapacitor device having a capacitor dielectric film of an oxidedielectric film such as a ferroelectric film and a high dielectric film,and a method for fabricating the semiconductor device.

In a recently accelerated trend in processing and storing massive dataresulting from development of digital technology, electronic equipmenthave been more and more highly developed, and therefore, semiconductordevices used in electronic equipment have been rapidly developed intheir refinement.

Accordingly, in order to realize a high degree of integration in adynamic RAM, a technique to use an oxide dielectric film as a capacitordielectric film instead of a conventionally used silicon oxide orsilicon nitride film has been widely studied and developed.

Also, in order to realize practical use of a nonvolatile RAM capable ofoperating at a lower voltage and writing/reading data at a higher speed,ferroelectric films having a spontaneous polarization characteristic areearnestly studied.

In a semiconductor memory using a ferroelectric film or a highdielectric film, in order to attain a high degree of integration of amegabit-class, stack-type memory cells are used instead ofconventionally used planer-type memory cells. The most significantproblem in employing the stack-type memory cells is preventing a contactface between a plug and a lower electrode of a capacitor device frombeing oxidized in high temperature annealing carried out in an oxygenatmosphere for crystallizing the ferroelectric film or the highdielectric film.

A conventional semiconductor device will now be described with referenceto FIG. 6A.

As shown in FIG. 6A, impurity diffusion layers 11 serving as the sourceand the drain are formed in a semiconductor substrate 10, and a gateelectrode 12 is formed on a region of the semiconductor substrate 10sandwiched between the impurity diffusion layers 11. The impuritydiffusion layers 11 and the gate electrode 12 together form atransistor.

A protection insulating film 13 is formed on the semiconductor substrate10 so as to cover the transistor, and a plug 14 of, for example,tungsten connected to one of the impurity diffusion layers 11 is formedin the protection insulating film 13.

An adhesive layer 15 of titanium having a lower face in contact with theupper face of the plug 14 is formed on the protection insulating film13. An oxygen barrier layer 16 of iridium oxide is formed on theadhesive layer 15, and a capacitor device composed of a capacitor lowerelectrode 17, a capacitor dielectric film 18 of a ferroelectric film anda capacitor upper electrode 19 is formed on the oxygen barrier layer 16.Accordingly, one of the impurity diffusion layers 11 of the transistoris electrically connected to the capacitor lower electrode 17 throughthe plug 14.

The oxygen barrier layer 16 has a function to prevent oxidation of theplug 14, and the adhesive layer 15 has a function to improve adhesionbetween the oxygen barrier layer 16 and the plug 14.

In order to crystallize the ferroelectric film used for forming thecapacitor dielectric film 18, it is necessary to carry out annealing ata temperature of 600 through 800 in an oxygen atmosphere. During thisannealing, a metal oxide film with high resistance is formed in thevicinity of the interface between the plug 14 and the adhesive layer 15,which disadvantageously increases the contact resistance between theplug 14 and the lower electrode 17.

Therefore, the present inventors have variously studied the cause of theformation of the metal oxide film in the vicinity of the interfacebetween the plug 14 and the adhesive layer 15, resulting in finding thefollowing:

FIG. 6B shows migration paths of oxygen atoms in the conventionalsemiconductor device, wherein denotes an oxygen atom and an arrowdenotes a migration path of the oxygen atom.

In the annealing for crystallizing the ferroelectric film used forforming the capacitor dielectric film 18, oxygen atoms included in theoxygen atmosphere are diffused into the capacitor dielectric film 18,then migrate through a first path for passing through the capacitorlower electrode 17 and the oxygen barrier layer 16 to reach the adhesivelayer 15 and through a second path for passing through a side portion ofthe capacitor dielectric film 18 to reach the adhesive layer 15, andfinally reach the plug 14.

Although the oxygen barrier layer 16 of iridium oxide is formed on theplug 14, the oxygen barrier layer 16 cannot definitely prevent thepassage of the oxygen atoms because the annealing for crystallization iscarried out in an oxygen atmosphere at a high temperature.

Also, when the oxygen atoms reach the adhesive layer 15, titaniumincluded in the adhesive layer 15 is easily oxidized into titaniumoxide, and hence, the oxygen atoms reach the plug 14 after thusoxidizing the adhesive layer. The oxygen atoms having reached the plug14 oxidize a metal, such as tungsten, included in the plug 14, whichdisadvantageously increases the contact resistance between the capacitorlower electrode 17 and the plug 14.

Furthermore, when the oxygen atoms reach the oxygen barrier layer 16,pin holes may be formed or the thickness is locally reduced in theoxygen barrier layer 16. Therefore, in a contact chain used for a testand including thousands or ten thousands of serially connected plugs 14,the resistance becomes abnormally high when the diameter of each plug 14is small.

SUMMARY OF THE INVENTION

In consideration of the aforementioned conventional problems, an objectof the invention is preventing contact resistance between a capacitorlower electrode and a plug from increasing by definitely preventingoxidation of the plug.

In order to achieve the object, the first semiconductor device of thisinvention comprises an impurity diffusion layer serving as a source or adrain of a transistor formed in a semiconductor substrate; a protectioninsulating film covering the transistor; a capacitor lower electrode, acapacitor dielectric film of an oxide dielectric film and a capacitorupper electrode successively formed on the protection insulating film; aplug buried in the protection insulating film for electricallyconnecting the impurity diffusion layer of the transistor to thecapacitor lower electrode; and an oxygen barrier layer formed betweenthe plug and the capacitor lower electrode, and the oxygen barrier layeris made from a composite nitride that is a mixture or an alloy of afirst nitride having a conducting property and a second nitride havingan insulating property.

In the first semiconductor device of the invention, the oxygen barrierlayer formed between the plug and the capacitor lower electrode is madefrom the composite nitride that is a mixture or an alloy of the firstnitride having a conducting property and the second nitride having aninsulating property. In an oxygen atmosphere at a high temperature, thesecond nitride having an insulating property is more highly reactivewith oxygen atoms than the first nitride having a conducting property.

Therefore, in crystallizing the capacitor dielectric film of the oxidedielectric film in an oxygen atmosphere at a high temperature, when theoxygen atoms diffuse into the oxygen barrier layer, the second nitridehaving an insulating property is rapidly reacted with the oxygen atomsto produce an oxide in a surface portion of the oxygen barrier layer.Since an oxide has a smaller particle size than a nitride, when thenitride is changed into the oxide, the migration paths of the oxygenatoms formed in the grain boundary of the nitride becomes complicatedand elongated, which makes it difficult for the oxygen atoms to diffusewithin the oxygen barrier layer. In other words, since an oxide layerfor preventing diffusion of the oxygen atoms is formed in the surfaceportion of the oxygen barrier layer, the function of the oxygen barrierlayer to prevent diffusion of the oxygen atoms can be improved.

When the nitride is changed into the oxide, the resistance of the oxygenbarrier layer may be increased. The composite nitride includes, however,the first nitride having a conducting property that is comparativelyless reactive with the oxygen atoms, which suppresses the increase ofthe resistance of the oxygen barrier layer.

Accordingly, while suppressing the increase of the resistance, theoxygen barrier layer can definitely prevent the diffusion of the oxygenatoms, resulting in definitely preventing oxidation of the plug.

In the first semiconductor device, the first nitride is preferably anitride of at least one of titanium, tantalum, cobalt, copper andgallium, and the second nitride is preferably a nitride of at least oneof aluminum, silicon, chromium, iron, zirconium and hafnium.

When the nitride of aluminum, silicon, chromium, iron, zirconium orhafnium is brought into contact with oxygen atoms at a high temperature,the nitride rapidly changes into an oxide, so as to prevent thediffusion of the oxygen atoms. Therefore, the function of the oxygenbarrier layer to prevent the diffusion of the oxygen atoms can bedefinitely improved. Furthermore, since the nitride of titanium,tantalum, cobalt, copper or gallium is difficult to oxidize even at ahigh temperature and is less degraded in its conducting property evenwhen oxidized, the increase of the resistance of the oxygen barrierlayer can be suppressed.

The first semiconductor device preferably further comprises an upperoxygen barrier layer formed between the oxygen barrier layer and thecapacitor lower electrode and made from a metal that has a conductingproperty when it is oxidized.

When the upper oxygen barrier layer of the metal that has a conductingproperty even when oxidized is thus formed on the oxygen barrier layer,two oxygen barrier layers are present on the plug. Therefore, thefunction to prevent the diffusion of the oxygen atoms can be furtherimproved and the increase of the resistance can be prevented.

In this case, the metal is preferably at least one of iridium,ruthenium, rhenium, osmium, rhodium, platinum and gold.

Thus, when the oxygen atoms diffuse into the upper oxygen barrier layer,a metal oxide layer that prevents the migration of the oxygen atoms anddoes not have very high resistance is formed in a surface portion of theupper oxygen barrier layer. Therefore, the diffusion of the oxygen atomscan be more effectively prevented.

The first semiconductor device preferably further comprises an upperoxygen barrier layer formed between the oxygen barrier layer and thecapacitor lower electrode and made from a metal oxide having aconducting property.

When the upper oxygen barrier layer of the metal oxide having aconducting property is thus formed on the oxygen barrier layer, twooxygen barrier layers are present on the plug. Therefore, the functionto prevent the diffusion of the oxygen atoms can be further improved andthe increase of the resistance can be prevented.

In this case, the metal oxide is preferably at least one of an iridiumoxide, a ruthenium oxide, a rhenium oxide, an osmium oxide and a rhodiumoxide.

Thus, the oxygen atoms diffusing through the upper oxygen barrier layerare prevented from migrating by the metal oxide, and hence, thediffusion of the oxygen atoms can be more effectively prevented.

The first semiconductor device preferably further comprises an upperoxygen barrier layer of a multi-layer structure composed of a firstmetal layer of a metal that has a conducting property when it isoxidized and a second metal layer of a metal oxide having a conductingproperty.

Thus, even when a defect is caused in one of the first metal layer andthe second metal layer, the other metal layer can prevent the passage ofthe oxygen atoms. Therefore, the diffusion of the oxygen atoms can bedefinitely prevented.

The second semiconductor device of this invention comprises an impuritydiffusion layer serving as a source or a drain of a transistor formed ina semiconductor substrate; a first protection insulating film coveringthe transistor; a plug buried in the first protection insulating filmand having a lower end electrically connected to the impurity diffusionlayer of the transistor; an oxygen barrier layer formed on the firstprotection insulating film and. having a lower face connected to anupper end of the plug; a capacitor lower electrode formed on the oxygenbarrier layer; a second protection insulating film formed on the firstprotection insulating film to cover peripheral faces of the oxygenbarrier layer and the capacitor lower electrode and having an upper faceplaced at substantially the same level as an upper face of the capacitorlower electrode; a capacitor dielectric film made from an oxidedielectric film formed on the capacitor lower electrode and the secondprotection insulating film and having a plane shape larger than a planeshape of the capacitor lower electrode; and a capacitor upper electrodeformed on the capacitor dielectric film.

In the second semiconductor device of this invention, the secondprotection insulating film is formed so as to cover the peripheral faceof the oxygen barrier layer. Therefore, in crystallizing the capacitordielectric film of the oxide dielectric film in an oxygen atmosphere ata high temperature, oxygen atoms included in the oxygen atmosphere passthrough the second protection insulating film before reaching the oxygenbarrier layer, and hence, the number of oxygen atoms that can reach theoxygen barrier layer can be reduced. Also, since the capacitordielectric film has a plane shape larger than that of the capacitorlower electrode, the oxygen atoms included in the oxygen atmospheremigrate by a long distance, namely, take a roundabout way, within thesecond protection insulating film before reaching the oxygen barrierlayer. Therefore, the number of oxygen atoms that can reach the oxygenbarrier layer can be further reduced.

Accordingly, the number of oxygen atoms that diffuse through the oxygenbarrier layer to reach the plug can be largely reduced, resulting indefinitely preventing the oxidation of the plug.

In the second semiconductor device, the oxygen barrier layer ispreferably made from a composite nitride that is a mixture or an alloyof a first nitride having a conducting property and a second nitridehaving an insulating property.

Thus, when the oxygen atoms pass through the second protectioninsulating film to reach the oxygen barrier layer, the second nitridehaving an insulating property is changed into an oxide in a surfaceportion of the oxygen barrier layer. Therefore, the oxygen atoms aredifficult to diffuse into the oxygen barrier layer, resulting in largelyimproving the function of the oxygen barrier layer to prevent thediffusion of the oxygen atoms.

The second semiconductor device preferably further comprises an upperoxygen barrier layer formed between the oxygen barrier layer and thecapacitor lower electrode and made from a metal that has a conductingproperty when it is oxidized.

Thus, two oxygen barrier layers are present on the plug, and hence, thefunction to prevent the diffusion of the oxygen atoms can be furtherimproved, and the increase of the resistance can be prevented.

The second semiconductor device preferably further comprises an upperoxygen barrier layer formed between the oxygen barrier layer and thecapacitor lower electrode and made from a metal oxide having aconducting property.

Thus, two oxygen barrier layers are present on the plug, and hence, thefunction to prevent the diffusion of the oxygen atoms can be furtherimproved, and the increase of the resistance can be prevented.

The method for fabricating a semiconductor device of this inventioncomprises the steps of forming an impurity diffusion layer serving as asource or a drain of a transistor in a semiconductor substrate; forminga first protection insulating film covering the transistor; burying, inthe first protection insulating film, a plug having a lower endelectrically connected to the impurity diffusion layer of thetransistor; forming, on the first protection insulating film, an oxygenbarrier layer having a lower face connected to an upper end of the plug;forming a capacitor lower electrode on the oxygen barrier layer;forming, on the first protection insulating film, a second protectioninsulating film covering the oxygen barrier layer and the capacitorlower electrode, and planarizing the second protection insulating film,whereby placing an upper face of the second protection insulating filmat substantially the same level as an upper face of the capacitor lowerelectrode; forming a capacitor dielectric film having a plane shapelarger than a plane shape of the capacitor lower electrode by depositingan oxide dielectric film on the capacitor lower electrode and the secondprotection insulating film and patterning the oxide dielectric film; andforming a capacitor upper electrode on the capacitor dielectric film.

In the method for fabricating a semiconductor device of this invention,after forming the second protection insulating film so as to cover theoxygen barrier layer and the capacitor lower electrode, the secondprotection insulating film is planarized so as to place the upper faceof the second protection insulating film at substantially the same levelas the upper face of the capacitor lower electrode. Therefore, thecapacitor dielectric film of the oxide dielectric film is crystallizedin an oxygen atmosphere at a high temperature with the peripheral faceof the oxygen barrier layer covered with the second protectioninsulating film, and hence, oxygen atoms included in the oxygenatmosphere pass through the second protection insulating film beforereaching the oxygen barrier layer. Also, since the capacitor dielectricfilm has a plane shape larger than that of the capacitor lowerelectrode, the oxygen atoms included in the oxygen atmosphere migrate bya long distance within the second protection insulating film beforereaching the oxygen barrier layer, and hence, the number of oxygen atomsthat can reach the oxygen barrier layer can be largely reduced.

Accordingly, the number of oxygen atoms that diffuse through the oxygenbarrier layer to reach the plug can be largely reduced, resulting indefinitely preventing oxidation of the plug.

In the method for fabricating a semiconductor device, the oxygen barrierlayer is preferably made from a composite nitride that is a mixture oran alloy of a first nitride having a conducting property and a secondnitride having an insulating property.

Thus, when the oxygen atoms pass through the second protectioninsulating film to reach the oxygen barrier layer, the second nitridehaving an insulating property is changed into an oxide in a surfaceportion of the oxygen barrier layer. Therefore, the oxygen atoms aredifficult to diffuse into the oxygen barrier layer, and hence, thefunction of the oxygen barrier layer to prevent the diffusion of theoxygen atoms can be largely improved.

The method for fabricating a semiconductor device preferably furthercomprises, between the step of forming the oxygen barrier layer and thestep of forming the capacitor lower electrode, a step of forming anupper oxygen barrier layer made from a metal that has a conductingproperty when it is oxidized.

Thus, since two oxygen barrier layers are present on the plug, thefunction to prevent the diffusion of the oxygen atoms can be furtherimproved, and increase of the resistance can be prevented.

The method for fabricating a semiconductor device preferably furthercomprises, between the step of forming the oxygen barrier layer and thestep of forming the capacitor lower electrode, a step of forming anupper oxygen barrier layer made from a metal oxide having a conductingproperty.

Thus, two oxygen barrier layers are present on the plug, the function toprevent the diffusion of the oxygen atoms can be further improved, andthe increase of the resistance can be prevented.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a cross-sectional view of a semiconductor device according toEmbodiment 1 of the invention, FIG. 1B is a cross-sectional view of asemiconductor device according to Embodiment 2 of the invention and FIG.1C is a cross-sectional view of a semiconductor device according toEmbodiment 3 of the invention;

FIGS. 2A, 2B and 2C are cross-sectional views for showing procedures ina method for fabricating the semiconductor device of Embodiment 2;

FIGS. 3A, 3B and 3C are cross-sectional views for showing otherprocedures in the method for fabricating the semiconductor device ofEmbodiment 2;

FIG. 4 is a diagram for showing the result of measurement of a failureoccurrence probability in a contact chain including serially connected1000 semiconductor devices;

FIG. 5 is a diagram for showing contact resistance corresponding toresistance of each plug; and

FIG. 6A is a cross-sectional view of a conventional semiconductor deviceand FIG. 6B is a cross-sectional view for explaining a problem of theconventional semiconductor device.

DETAILED DESCRIPTION OF THE INVENTION

Embodiment 1

A semiconductor device according to Embodiment 1 of the invention willnow be described with reference to FIG. 1A.

As shown in FIG. 1A, a pair of impurity diffusion layers 101 serving asthe source and the drain of a transistor are formed in a semiconductorsubstrate 100, and a gate electrode 102 of the transistor is formed on aregion of the semiconductor substrate 100 sandwiched between the pair ofimpurity diffusion layers 101.

A first protection insulating film 103 of, for example, a TEOS-O₃ filmis formed on the semiconductor substrate 100 so as to cover thetransistor, and a plug 107 of tungsten having a lower end connected toone of the pair of impurity diffusion layers 101 is buried in the firstprotection insulating film 103. The plug 107 includes a barrier metalcomposed of an outside titanium film with a thickness of, for example,30 nm and an inside titanium nitride film with a thickness of, forexample, 50 nm. The upper face of the plug 107 is placed atsubstantially the same level as the upper face of the first protectioninsulating film 103.

An oxygen barrier layer 108A with a thickness of 20 nm through 200 nmhaving a lower face connected to the upper end of the plug 107 is formedon the first protection insulating film 103. The oxygen barrier layer108A is made from a composite nitride that is a mixture or an alloy of afirst nitride having a conducting property and a second nitride havingan insulating property. The first nitride may be a nitride of at leastone of titanium, tantalum, cobalt, copper and gallium, and the secondnitride may be a nitride of at least one of aluminum, silicon, chromium,iron, zirconium and hafnium.

A capacitor lower electrode 110A of a platinum film with a thickness of,for example, 50 nm is formed on the oxygen barrier layer 108A.

The peripheral faces of the oxygen barrier layer 108A and the capacitorlower electrode 110A are covered with a second protection insulatingfilm 111, and the upper face of the second protection insulating film111 is placed at substantially the same level as the upper face of thecapacitor lower electrode 110A.

A capacitor dielectric film 112A of an oxide dielectric film such as aferroelectric film and a high dielectric film with a thickness of 10 nmthrough 200 nm is formed on the second protection insulating film 111 soas to have a lower face in contact with the capacitor lower electrode110A. The capacitor dielectric film 112A is in contact with thecapacitor lower electrode 110A and has a plane shape larger than that ofthe capacitor lower electrode 110A. The oxide dielectric film is notspecified in its kind, and may be a ferroelectric film having abismuth-layered perovskite structure such as SrBi₂(Ta_(1−x)Nb_(x))O₉, ora film of lead zirconate titanate, strontium barium titanate, tantalumpentaoxide or the like.

A capacitor upper electrode 113A of a platinum film with a thickness of,for example, approximately 50 nm is formed on the capacitor dielectricfilm 112A, and the capacitor dielectric film 112A and the capacitorupper electrode 113A are covered with a third protection insulating filmnot shown.

In the semiconductor device of Embodiment 1, the oxygen barrier layer108A of the composite nitride that is a mixture or an alloy of the firstnitride having a conducting property and the second nitride having aninsulating property is formed between the plug 107 and the capacitorlower electrode 110A. In an oxygen atmosphere at a high temperature, thesecond nitride having an insulating property is more highly reactivewith oxygen atoms than the first nitride having a conducting property.Therefore, in crystallizing the capacitor dielectric film 112A of theoxide dielectric film in an oxygen atmosphere at a high temperature,when oxygen atoms are diffused into the oxygen barrier layer 108A, thesecond nitride having an insulating property is rapidly reacted with theoxygen atoms to produce an oxide in a surface portion of the oxygenbarrier layer 108A. Since an oxide has a smaller particle size than anitride, when the nitride is changed into the oxide, migration paths ofthe oxygen atoms formed in the grain boundary of the nitride becomecomplicated and elongated, which makes difficult for the oxygen atoms todiffuse into the oxygen barrier layer 108A. In other words, an oxidelayer for preventing the diffusion of the oxygen atoms is formed in thesurface portion of the oxygen barrier layer 108A, and hence, thefunction of the oxygen barrier layer 10A for preventing the diffusion ofthe oxygen atoms can be improved.

When the nitride is changed into the oxide, the resistance of the oxygenbarrier layer 108A may be increased. However, since the compositenitride includes the first nitride having a conducting property that iscomparatively less reactive with the oxygen atoms, the increase of theresistance of the oxygen barrier layer 108A can be suppressed.

Accordingly, while suppressing the increase of the resistance, theoxygen barrier layer 108A can definitely prevent the diffusion of theoxygen atoms, and therefore, oxidation of the plug 107 can be definitelyprevented.

Furthermore, since the second nitride included in the oxygen barrierlayer 108A is made from a nitride of aluminum, silicon, chromium, iron,zirconium or hafnium, when it is brought into contact with the oxygenatoms at a high temperature, it is rapidly changed into the oxide,resulting in preventing the diffusion of the oxygen atoms. Accordingly,the function of the oxygen barrier layer 108A to prevent the diffusionof the oxygen atoms can be definitely improved.

Moreover, since the first nitride included in the oxygen barrier layer108A is made from a nitride of titanium, tantalum, cobalt, copper orgallium, it is difficult to oxide even at a high temperature, and evenwhen it is oxidized, its conducting property is less degraded.Therefore, the increase of the resistance of the oxygen barrier layer108A can be suppressed.

Also, since the peripheral face of the oxygen barrier layer 108A iscovered with the second protection insulating film 111, in crystallizingthe capacitor dielectric film 112A of the oxide dielectric film in anoxygen atmosphere at a high temperature, the oxygen atoms included inthe oxygen atmosphere pass through the second protection insulating film111 before reaching the oxygen barrier layer 108A. Therefore, the numberof oxygen atoms that can reach the oxygen barrier layer 108A can bereduced.

In addition, since the capacitor dielectric film 112A has a plane shapelarger than that of the capacitor lower electrode 110A, the oxygen atomsincluded in the oxygen atmosphere migrate by a long distance, namely,take a roundabout way, within the second protection insulating film 111before reaching the oxygen barrier layer 108A. Therefore, the number ofoxygen atoms that can reach the oxygen barrier layer 108A can be furtherreduced.

Accordingly, since the number of oxygen atoms that are diffused throughthe oxygen barrier layer 108A to reach the plug 107 can be largelyreduced, the oxidation of the plug 107 can be definitely prevented.

Embodiment 2

A semiconductor device according to Embodiment 2 of the invention willnow be described with reference to FIG. 1B.

As shown in FIG. 1B, a pair of impurity diffusion layers 101 serving asthe source and the drain of a transistor are formed in a semiconductorsubstrate 100, and a gate electrode 102 of the transistor is formed on aregion of the semiconductor substrate 100 sandwiched between the pair ofimpurity diffusion layers 101.

A first protection insulating film 103 of, for example, a TEOS-O₃ filmis formed on the semiconductor substrate 100 so as to cover thetransistor, and a plug 107 of tungsten having a lower end connected toone of the pair of impurity diffusion layers 101 is buried in the firstprotection insulating film 103. The plug 107 includes a barrier metalcomposed of, for example, a titanium film and a titanium nitride film,and the upper face of the plug 107 is placed at substantially the samelevel as the upper face of the first protection insulating film 103.

An oxygen barrier layer 108A with a thickness of 20 nm through 200 nmhaving a lower face connected to the upper end of the plug 107 is formedon the first protection insulating film 103. The oxygen barrier layer108A is made from a composite nitride that is a mixture or an alloy of afirst nitride having a conducting property and a second nitride havingan insulating property. The first nitride may be a nitride of at leastone of titanium, tantalum, cobalt, copper and gallium, and the secondnitride may be a nitride of at least one of aluminum, silicon, chromium,iron, zirconium and hafnium.

An upper oxygen barrier layer 109A with a thickness of, for example, 100nm of a metal that has a conducting property even when oxidized isformed on the oxygen barrier layer 108A. The metal that has a conductingproperty even when oxidized may be at least one of iridium, ruthenium,rhenium, osmium, rhodium, platinum and gold.

A capacitor lower electrode 110A of a platinum film with a thickness of,for example, 50 nm is formed on the upper oxygen barrier layer 109A. Theperipheral faces of the oxygen barrier layer 108A, the upper oxygenbarrier layer 109A and the capacitor lower electrode 110A are coveredwith a second protection insulating film 111, and the upper face of thesecond protection insulating film 111 is placed at substantially thesame level as the upper face of the capacitor lower electrode 110A.

A capacitor dielectric film 112A of an oxide dielectric film such as aferroelectric film and a high dielectric film with a thickness of 10 nmthrough 200 nm is formed on the second protection insulating film 111 soas to have a lower face in contact with the capacitor lower electrode110A. The capacitor dielectric film 112A is in contact with thecapacitor lower electrode 110A and has a plane shape larger than that ofthe capacitor lower electrode 110A. The oxide dielectric film is notspecified in its kind, and may be a ferroelectric film having abismuth-layered perovskite structure such as SrBi₂(Ta_(1−x)Nb_(x))O₉, ora film of lead zirconate titanate, strontium barium titanate, tantalumpentaoxide or the like.

A capacitor upper electrode 113A of a platinum film with a thickness of,for example, approximately 50 nm is formed on the capacitor dielectricfilm 112A, and the capacitor dielectric film 112A and the capacitorupper electrode 113A are covered with a third protection insulating filmnot shown.

In the semiconductor device of Embodiment 2, the upper oxygen barrierlayer 109A is formed between the oxygen barrier layer 108A and thecapacitor lower electrode 110A. Therefore, the diffusion of the oxygenatoms can be more effectively prevented than in the semiconductor deviceof Embodiment 1, and hence, the oxidation of the plug 107 can be moredefinitely prevented.

In the case where the upper oxygen barrier layer 109A is made from atleast one of iridium, ruthenium, rhenium, osmium, rhodium, platinum andgold, a metal oxide layer that prevents the migration of the oxygenatoms and does not largely increase the resistance is formed in asurface portion of the upper oxygen barrier layer 109A when the oxygenatoms are diffused into the upper oxygen barrier layer 109A.Accordingly, the diffusion of the oxygen atoms can be more definitelyprevented.

Instead of the metal that has a conducting property even when oxidized,a metal oxide having a conducting property including at least one of aniridium oxide, a ruthenium oxide, a rhenium oxide, an osmium oxide and arhodium oxide may be used as the metal included in the upper oxygenbarrier layer 109A.

Embodiment 3

A semiconductor device according to Embodiment 3 of the invention willnow be described with reference to FIG. 1C.

As shown in FIG. 1C, a pair of impurity diffusion layers 101 serving asthe source and the drain of a transistor are formed in a semiconductorsubstrate 100, and a gate electrode 102 of the transistor is formed on aregion of the semiconductor substrate 100 sandwiched between the pair ofimpurity diffusion layers 101.

A first protection insulating film 103 of, for example, a TEOS-O₃ filmis formed on the semiconductor substrate 100 so as to cover thetransistor, and a plug 107 of tungsten having a lower end connected toone of the pair of impurity diffusion layers 101 is buried in the firstprotection insulating film 103. The plug 107 includes a barrier metalcomposed of, for example, a titanium film and a titanium nitride film.The upper face of the plug 107 is placed at substantially the same levelas the upper face of the first protection insulating film 103.

An oxygen barrier layer 108A with a thickness of 20 nm through 200 nmhaving a lower face connected to the upper end of the plug 107 is formedon the first protection insulating film 103. The oxygen barrier layer108A is made from a composite nitride that is a mixture or an alloy of afirst nitride having a conducting property and a second nitride havingan insulating property. The first nitride may be a nitride of at leastone of titanium, tantalum, cobalt, copper and gallium, and the secondnitride may be a nitride of at least one of aluminum, silicon, chromium,iron, zirconium and hafnium.

A first upper oxygen barrier layer 114A of a metal that has a conductingproperty even when oxidized and a second upper oxygen barrier layer 115Aof a metal oxide having a conducting property are successively formed onthe oxygen barrier layer 108A. Either of the first upper oxygen barrierlayer 114A and the second upper oxygen barrier layer 115A may bedisposed below. The metal that has a conducting property even whenoxidized used for forming the first upper oxygen barrier layer 114A maybe at least one of iridium, ruthenium, rhenium, osmium, rhodium,platinum and gold. The metal oxide having a conducting property used forforming the second upper oxygen barrier layer 115A may be at least oneof an iridium oxide, a ruthenium oxide, a rhenium oxide, an osmium oxideand a rhodium oxide.

A capacitor lower electrode 110A of a platinum film with a thickness of,for example, 50 nm is formed on the second upper oxygen barrier layer115A. The peripheral faces of the oxygen barrier layer 108A, the firstupper oxygen barrier layer 114A, the second upper oxygen barrier layer115A and the capacitor lower electrode 110A are covered with a secondprotection insulating film 111, and the upper face of the secondprotection insulating film 111 is placed at substantially the same levelas the upper face of the capacitor lower electrode 110A.

A capacitor dielectric film 112A of an oxide dielectric film such as aferroelectric film and a high dielectric film with a thickness of 10 nmthrough 200 nm is formed on the second protection insulating film 111 soas to have a lower face in contact with the capacitor lower electrode110A. The capacitor dielectric film 112A is in contact with thecapacitor lower electrode 110A and has a plane shape larger than that ofthe capacitor lower electrode 110A. The oxide dielectric film is notspecified in its kind, and may be a ferroelectric film having abismuth-layered perovskite structure such as SrBi₂(Ta_(1−x)Nb_(x))O₉, ora film of lead zirconate titanate, strontium barium titanate, tantalumpentaoxide or the like.

A capacitor upper electrode 113A of a platinum film with a thickness of,for example, approximately 50 nm is formed on the capacitor dielectricfilm 112A, and the capacitor dielectric film 112A and the capacitorupper electrode 113A are covered with a third protection insulating filmnot shown.

In the semiconductor device of Embodiment 3, a multi-layer structureincluding the first upper oxygen barrier layer 114A and the second upperoxygen barrier layer 115A is formed between the oxygen barrier layer108A and the capacitor lower electrode 110A. Therefore, the diffusion ofthe oxygen atoms can be more effectively prevented than in thesemiconductor device of Embodiment 2. As a result, the oxidation of theplug 107 can be further definitely prevented.

Embodiment 4

In Embodiment 4 of the invention, a method for fabricating thesemiconductor device of Embodiment 2 will be described. A method forfabricating the semiconductor device of Embodiment 1 or 3 is basicallythe same as the fabrication method for the semiconductor device ofEmbodiment 2 and hence is omitted.

First, as shown in FIG. 2A, a gate electrode 102 of a transistor isformed on a semiconductor substrate 100 by a known method, and a pair ofimpurity diffusion layers 101 serving as the source and the drain of thetransistor are formed in regions of the semiconductor substrate 100 onboth sides of the gate electrode 102.

Next, after forming a first protection insulating film 103 of, forexample, a TEOS-O₃ film on the semiconductor substrate 100 so as tocover the transistor, the first protection insulating film 103 isplanarized by CMP. Thereafter, the first protection insulating film 103is selectively etched, so as to form a plug opening 104 by exposing oneof the pair of impurity diffusion layers 101.

Then, as shown in FIG. 2B, a barrier metal 105 composed of a lowertitanium film (with a thickness of 30 nm) and an upper titanium nitridefilm (with a thickness of 50 nm) and a tungsten film 106 (with athickness of 600 nm) are successively deposited on the first protectioninsulating film 103 so as to fill the plug opening 104. Thereafter,portions of the barrier metal 105 and the tungsten film 106 exposedoutside the plug opening 104 are removed by the CMP, thereby forming aplug 107 as shown in FIG. 2C.

Next, as shown in FIG. 2C, an oxygen barrier layer 108 with a thicknessof 20 nm through 200 nm of a composite nitride that is a mixture or analloy of a first nitride having a conducting property and a secondnitride having an insulating property is deposited on the firstprotection insulating film 103. The first nitride may be a nitride of atleast one of titanium, tantalum, cobalt, copper and gallium, and thesecond nitride may be a nitride of at least one of aluminum, silicon,chromium, iron, zirconium and hafnium.

Subsequently, an upper oxygen barrier layer 109 with a thickness of, forexample, 100 nm of a metal that has a conducting property even whenoxidized is deposited on the oxygen barrier layer 108. The metal thathas a conducting property even when oxidized may be at least one ofiridium, ruthenium, rhenium, osmium, rhodium, platinum and gold. Insteadof the metal that has a conducting property even when oxidized, theupper oxygen barrier layer 109 may be made from a metal oxide having aconducting property including at least one of an iridium oxide, aruthenium oxide, a rhenium oxide, an osmium oxide and a rhodium oxide.

Then, a first platinum film 110 with a thickness of, for example,approximately 50 nm is deposited on the upper oxygen barrier layer 109by sputtering.

Next, as shown in FIG. 3A, the first platinum film 110, the upper oxygenbarrier layer 109 and the oxygen barrier layer 108 are successivelypatterned, thereby forming a capacitor lower electrode 110A from thefirst platinum film 110 and forming a patterned upper oxygen barrierlayer 109A and a patterned oxygen barrier layer 108A.

Then, a second protection insulating film 111 of, for example, a TEOS-O₃film with a thickness of 400 nm is formed on the first protectioninsulating film 103 so as to cover the capacitor lower electrode 110A,the patterned upper oxygen barrier layer 109A and the patterned oxygenbarrier layer 108A.

Subsequently, as shown in FIG. 3B, the second protection insulating film111 is planarized by the CMP so as to place the upper face of the secondprotection insulating film 111 at substantially the same level as theupper face of the capacitor lower electrode 110A. Then, an oxidedielectric film 112 of a ferroelectric film or a high dielectric filmwith a thickness of 10 nm through 200 nm is deposited on the planarizedsecond protection insulating film 111. The oxide dielectric film is notspecified in its kind, and may be a ferroelectric film having abismuth-layered perovskite structure such as SrBi₂(Ta_(1−x)Nb_(x))O₉, ora film of lead zirconate titanate, strontium barium titanate, tantalumpentaoxide or the like. Also, the method for forming the oxidedielectric film 112 may be metal organic decomposition (MOD), metalorganic chemical vapor deposition (MOCVD), the sputtering or the like.

Next, a second platinum film 113 with a thickness of, for example,approximately 50 nm is deposited on the oxide dielectric film 112 by thesputtering.

Then, as shown in FIG. 3C, the second platinum film 113 and the oxidedielectric film 112 are successively patterned, so as to form acapacitor upper electrode 113A from the second platinum film 113 and acapacitor dielectric film 112A from the oxide dielectric film 112 bothin a plane shape larger than that of the upper oxygen barrier layer 109Aand the oxygen barrier layer 10A. In this case, since the secondplatinum film 113 and the oxide dielectric film 112 are formed on theplanarized second protection insulating film 111, there does not arise aproblem of etching residue after patterning the second platinum film 113and the oxide dielectric film 112.

Thereafter, the resultant semiconductor substrate 100 is subjected toannealing carried out in an oxygen atmosphere at a temperature of 600through 800 for 10 through 60 minutes, thereby crystallizing thecapacitor dielectric film 112A.

During the annealing for crystallization oxygen atoms included in theoxygen atmosphere, which are to diffuse through the upper oxygen barrierlayer 109A and the oxygen barrier layer 108A to reach the plug 107, areobstructed not only by the upper oxygen barrier layer 109A made from themetal that has a conducting property even when oxidized or the metaloxide having a conducting property but also by the oxygen barrier layer108A made from the composite nitride that is a mixture or an alloy ofthe first nitride having a conducting property and the second nitridehaving an insulating property. As a result, the oxygen atoms minimallyreach the plug 107.

The mechanism of the upper oxygen barrier layer 109A for preventingdiffusion of the oxygen atoms is described in Embodiment 2, and themechanism of the oxygen barrier layer 108A for preventing the diffusionof the oxygen atoms is described in Embodiment 1.

Also, during the annealing for the crystallization, the oxygen atomsincluded in the oxygen atmosphere pass through the second protectioninsulating film 111 before reaching the upper oxygen barrier layer 109Aand the oxygen barrier layer 108A. Therefore, the number of oxygen atomsthat can reach the upper oxygen barrier layer 109A and the oxygenbarrier layer 108A is reduced.

Furthermore, since the plane shape of the capacitor dielectric film 112Ais larger than that of the capacitor lower electrode 110A, the oxygenatoms included in the oxygen atmosphere migrate by a long distancewithin the second protection insulating film 111 before reaching theupper oxygen barrier layer 109A and the oxygen barrier layer 108A.Therefore, the number of oxygen atoms that can reach the upper oxygenbarrier layer 109A and the oxygen barrier layer 108A is further reduced.

Accordingly, the number of oxygen atoms that can reach the plug 107 canbe thus largely reduced, so as to definitely prevent oxidation of theplug 107.

Now, an electric characteristic test carried out on a conventionalsemiconductor device and the semiconductor device of Embodiment 2 willbe described.

First, by using the structure of the conventional semiconductor deviceor the semiconductor device of Embodiment 2, contact chains are preparedeach by serially connecting 1000 semiconductor devices through plugs bysharing impurity diffusion layers and capacitor lower electrodes (sothat an (n−1)th transistor can share an impurity diffusion layer with annth transistor and the nth transistor can share a capacitor lowerelectrode with an (n+1)th transistor) with the diameters of the plugsvaried from 0.22 ìm to 0.30 ìm by 0.01 {grave over (l)}m in therespective constant chains. The annealing for crystallizing thecapacitor dielectric films is carried out by keeping the semiconductorsubstrates at a substrate temperature of 700 for 1 hour in an oxygenatmosphere.

FIG. 4 shows a failure occurrence probability measured in a test inwhich every contact chain including the serially connected 1000semiconductor devices is decided to be faulty when its resistanceobtained in applying a predetermined voltage to the both ends thereofexceeds a predetermined value. It is understood from FIG. 4 that thefailure occurrence probability is remarkably low in using thesemiconductor device of Embodiment 2. For example, when the plug has adiameter of 0.24 ìm, the failure occurrence probability is 0% in thecontact chain using the semiconductor device of Embodiment 2 while thefailure occurrence probability is 98% in the contact chain using theconventional semiconductor device. Thus, the characteristic can beremarkably improved.

FIG. 5 shows contact resistance corresponding to resistance of each plugcalculated by dividing, by 1000, resistance obtained by applying apredetermined voltage to the both ends of each contact chain includingthe serially connected 1000 semiconductor devices. When the plug has adiameter of 0.24 ìm, the contact resistance of the semiconductor deviceof Embodiment 2 is 400 Ù while the contact resistance is 4 kÙ or more inthe conventional semiconductor device. In this manner, according toEmbodiment 2, contact resistance applicable to an actual device can beobtained even when high temperature annealing is carried out in anoxygen atmosphere.

What is claimed is:
 1. A semiconductor device comprising: a protectioninsulating film formed on a substrate; a capacitor lower electrode, acapacitor dielectric film of an oxide dielectric film and a capacitorupper electrode successively formed on said protection insulating film;a plug buried in said protection insulating; and an oxygen barrier layerformed between said plug and said capacitor lower electrode so as toelectrically connect said plug and said capacitor lower electrode;wherein said oxygen barrier layer is made from a composite nitride thatis a mixture or an alloy of a first nitride particle having a conductingproperty and a second nitride particle having an insulating property. 2.The semiconductor device of claim 1, wherein said first nitride is anitride of at least one of titanium, tantalum, cobalt, copper andgallium, and said second nitride is a nitride of at least one ofaluminum, silicon, chromium, iron, zirconium and hafnium.
 3. Thesemiconductor device of claim 1, further comprising an upper oxygenbarrier layer formed between said oxygen barrier layer and saidcapacitor lower electrode and made from a metal that has a conductingproperty when it is oxidized.
 4. The semiconductor device of claim 3,wherein said metal is at least one of iridium, ruthenium, rhenium,osmium, rhodium, platinum and gold.
 5. The semiconductor device of claim1, further comprising an upper oxygen barrier layer formed between saidoxygen barrier layer and said capacitor lower electrode and made from ametal oxide having a conducting property.
 6. The semiconductor device ofclaim 5, wherein said metal oxide is at least one of an iridium oxide, aruthenium oxide, a rhenium oxide, an osmium oxide and a rhodium oxide.7. The semiconductor device of claim 1, further comprising an upperoxygen barrier layer of a multi-layer structure composed of a firstmetal layer of a metal that has a conducting property when it isoxidized and a second metal layer of a metal oxide having a conductingproperty.
 8. A semiconductor device comprising: a first protectioninsulating film formed on a substrate; a plug buried in said firstprotection insulating film; an oxygen barrier layer formed on said firstprotection insulating film and having a lower face in contact with anupper end of said plug a capacitor lower electrode formed on said oxygenbarrier layer; a second protection insulating film formed on said firstprotection insulating film to cover peripheral faces of said oxygenbarrier layer and said capacitor lower electrode and having an upperface placed at substantially the same level as an upper face of saidcapacitor lower electrode; a capacitor dielectric film made from anoxide dielectric film formed on said capacitor lower electrode and saidsecond protection insulating film and having a plane shape larger than aplane shape of said capacitor lower electrode, and having a flatsurface; and a capacitor upper electrode formed on said capacitordielectric film.
 9. The semiconductor device of claim 8, wherein saidoxygen barrier layer is made from a composite nitride that is a mixtureor an alloy of a first nitride having a conducting property and a secondnitride having an insulating property.
 10. The semiconductor device ofclaim 8, further comprising an upper oxygen barrier layer formed betweensaid oxygen barrier layer and said capacitor lower electrode and madefrom a metal that has a conducting property when it is oxidized.
 11. Thesemiconductor device of claim 8, further comprising an upper oxygenbarrier layer formed between said oxygen barrier layer and saidcapacitor lower electrode and made from a metal oxide having aconducting property.